Ultrasonic angle measurement system

ABSTRACT

An ultrasonic angle measuring system having three systemspatially fixed receivers and two transmitters mounted on a helmet wherein the time lapse information at the receivers of signals from the transmitters establishes the location and orientation of the helmet with respect to a reference position.

United States Patent [191 Stoutmeyer Dec. 4, 1973 ULTRASONIC ANGLEMEASUREMENT [56] References Cited SYSTEM UNITED STATES PATENTS [75]Inventor: Ronald G. Stoutmeyer, China Lake, 3,569,920 3/1971 Antman340/5 R Calif. 3,205,475 9/1965 FOSS 340/6 R [73] Asslgneer r igz;fiitxg; i Primary, Examiner-Richard A. Farley Z wuhinium D C y Attorney-R.S. Sciascia et al.

[22] Fileci: 7 Apr. 10, 1 972 W 57 ABSTRACT [21] App]. No.: 242,540 Anultrasonic angle measuring system having three system-spatiallyfixedreceivers and two transmitters mounted on a helmet wherein the timelapse informa- [gf] (gill "(gall/1561!; tion at the receivers of Signalsfrom the transmitters d 5 establishes the location and orientation ofthe helmet o E g 343/115 C with respect to a reference position.

' 8 Claims, 2 Drawing Figures TRANSMITTER TRANSMITTER H RECEIVER aHELMET MOUNTED GHT i I lim t! "f HL fl 1 ,"J' I i- RECEIVER TRANSMITTER1 TRANSMITTER RECEIVER HELMET l RECEIVER Fig I 4* p E l l I I a B p +Y rr I -/\\L I 0 i +X SPHERICAL POLAR xsmcos0 X=pCOSoz Z=pCOS Z=pCOSE Fig.2

ULTRASONIC ANGLEMEASUREMENT SYSTEM BACKGROUND OF THE INVENTION Thepresent invention relates to the field of headcoupled aiming devicesand, specifically, to pilot aimed missiles wherein the missile seekerhead is slaved to the pilots helmet such that the pilots line-of-sightis the missiles aim direction.

If the pilot is provided with a sight on his helmet that is independentof eye movement, such as the sight dis closed in U. S. Pat. No.3,633,988, entitled Helmet- Mounted Holographic Aiming Sight, filed July10, 1970, by Reed A. Farrar, the problem of measuring'the pilotsline-of-sight reduces to oneof tracking his helmet, i.e., sensing theaim directon of the helmet. lmportant considerations, other thanaccuracy, for any helmet tracking scheme are the pilots safety andcomfort, and cockpit space. Pilots safety and comfort imposerestrictions on helmet weight, mechanical connections to the helmet, andfracturable material near the eyes. Cockpit space restricts the use ofmechanical linkage and optical leverage. Of course, in any design thepilots vision should not be obstructed by objects on the helmet or inthe cockpit.

Two previous devices for measuring the position and orientation of thepilots helmetwithin the cockpit are U, S. Pat. No. 3,617,015 entitledHead-Coupled Missile-Aiming Device by Floyd -A. Kinder, a device whereina mechanical linkage couples the pilots head to a system-spatially fixedcockpit reference; and U. S. Pat. No. 3,678,283, entitled RadiationSensitive Optical Tracker, filed Oct. 22, 1970, by Kenneth B. LaBaw, adevice wherein at least two light sources and one photodetector aresystem-spatially fixed and one light source and one photodetector aremounted on the pilotshelmet. The patent and the application are assignedto the U. S. Government and are incorporated herein as backgroundmaterial.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of the preferredembodiment of the present invention; and

FIG. 2 is a schematic diagram of the spherical coordinate system (A) andpolar space coordinate system (B) which maybe used to transformequations in the polar space coordinate system to the sphericalcoordinate system, if transformation is desired.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention, shown inFIG. I, is a system for acoustically locating the pilots helmet withinthe cockpit and measuring the pilots line-of-sight.

Two ultrasonic wave emitting transmitters H and H, are positioned on aside of the helmet. The line determined .by the H, and II, should bealigned parallel to the optical axis of a helmet sight, as shown inFIG. 1. That is, the transmitters should be positioned on the helmetsuch that they define a line parallel to the pilot's line-of-sight. And,three ultrasonic wave receiving devices P,, P,, and P, are mounted in areference plane on the cockpits structure.

The approach used in the present invention is to determine the distancefrom H 1 to P to P and to P and from H 1: to P to Pg. and to P Knowingthese distances. the distance between H, and H and the locations of P,,P,, and P the pilots line-of-sight can be ascertained.

The frequency at the wave transmitter H can be the same as, or differentthan, the frequency of the wave emitted by transmitter H In either case,the transmitters are pulsed and the time it takes for the wave from eachto arrive in each of the receivers is measured. That time indicates thedistance from the transmitter to the receiver. If the frequency of thewave emitted by H 1 and H: are the same, H should not be pulsed untilthe wave from H, is received by P P and P and viceversa. otherwise thesystem might confuse the wave 7 from H with the wave from Hg. A computercan be included in the system to obtain the distances of interest byprocessing the information generated and performing the mathematicalcomputations herein disclosed.

The geometry of the system and the equations to be solved will now bediscussed. Since we know that the distance between two points can bemeasured by the elapsed time of acoustical energy passing between thepoints, the following simplified geometrical relationship and equationsare recognized by the inventor to define the pointing vector of a linedrawn between the two points, i.e., two acoustical transducers mountedon an operator's helmet. As a result, the operators head position andorientation is defined.

The present approach consists of fixed receiving devices P P and Plocated in a reference plane A, and transmitting devices H and H mountedon a subjects head via a helmet or headpiece supporting structure. Theline determined by transmitters H, and H, is first aligned parallel tothe optical axis of a collimated sightingdevice also mounted on thehelmet. FIG. 1 shows such a configuration in an inverted cartesiancoordinate system, which is the coordinate system used in aircraft.Distances s s s s s and s;' are measured acoustically in the mannerdiscussed above.

From the geometry of FIG. 1 the following equations can be written fordistances s s and s to transmitter H.

s,==x+y +z s (x a) Y (1'. s;, =(x+a)+y +(z-l a) Solving these threeequations for .1: results in:

x s s l4a And, in a similar manner solving for z:

z s, s 2s 4a'l4a Repeating the computations for distances a, s and totransmitter H results in the following;

Note that in the specified coordinatesystem the direction cosines of theline between H, and H, are;

case: x x'ld cos: z z'ld Where d is the known distance between H, and HThat is,

cos d) cos e cos cos a/sin dz Note that I 90 4a. Therefore,

sin I cos 6,

sin I z z'/d.

And, note also that sin ti) sin s, with sin e As a result,

'cos6=xx/ m I Sin' (z z'ld),

0 and I can now be recognized as the spherical coordinate angles of theline drawn between H, and H As a result, using the approach of thepreferred embodiment of the present invention, error in the orientationof the pilots helmet will not be dependent on translational motion,i.e., motion in the x, y, or 1 directions. As long as the pilot's headremains in his normal head-motion box, his line of sight will be definedby information obtained from the preferred embodiment of the presentinvention, which information is substantially independent of the x, y,and z position of the pilots helmet.

The present invention operates as follows: Transmitters H, and H bothemit ultrasonic waves. The waves transmitted by transmitter H, arereceived by system-spatially fixed receivers P,, P and P, with thereceiver nearest the transmitter receiving the pulsed wave first. Thatis, the receiver which is nearest transmitter H, will receivethe'emitted waves first, the second nearest receiver will receive thewaves second, and the farthest receiver from the transmitter willreceive the waves last. Knowing the positions of receivers P,, P andP,,, the moment transmitter H, transmitted the wave, and the time ittook the wave to reach receivers P,, P,, and P the distances fromtransmitter H, to receivers P,, P and P, can be determined. Thereby, theposition of transmitter H, with respect to the systems-spatially fixedcoordinate system is defined. Likewise, the position H, with respect tothe systemspatially fixed coordinate system can be determined.

By knowing the position of transmitters H, and H 6 the distance betweenthem, and the relationship of the line defined by the points in spaceoccupied by the transmitters and the pilot's line of sight, the pilotsline of sight can be determined. For convenience, the mathematicalcomputations necessary to define the pilots line of sight should beperformed by a computer, and where the present invention is used in anaircraft, preferably an on-board computer.

The present invention has the advantages of being a very light devicewhich, when used in an aircraft, does not limit .the pilots normalhead-motion box. It does not include any mechanical connections to thepilot which could cause discomfort and limit the operators freedom ofmovement. Nor does it depend on iliumina tion sources which dependence,likewise, would restrict the operators freedom of movement' What isclaimed is:

1. An acoustical tracker system'for determining the position andorientation of an object, comprising:

first and second means attached to said object for radiating ultrasonicwaves;

first, second, and third ultrasonic wave detecting meanssystem-spatially fixed for detecting said radiated ultrasonic waves andproviding outputs in response thereto; and

means coupled to said radiating means and said detecting means forprocessing said detecting means outputs, electronically calculating thedistances from each said radiating means to each said detecting means,and providing an output of information defining the position andorientation of said object.

2. The tracker of claim 1 wherein the points in space occupied by saidfirst, second, and third detecting means define a plane, and the secondand third detecting means are equally spaced from the first detectingmeans.

3. The tracker of claim 1 wherein said object is an operators helmet andsaid tracker further comprises a helmet mounted sight which isindependent of operator eye movement, such that thel tracker determinesthe orientation of the helmet and, thereby, the operators line-of-sight.

4. The tracker of claim 3 wherein the points on the helmet occupied bysaid first and second radiating means define a line which is parallel tothe operators line-of-sight.

5. The tracker of claim 4 wherein the points in space occupied by saidfirst, second, and third detecting means defines a plane, and the secondand third detecting means are equally spaced from the first detectingmeans.

6. The tracker of claim 5 wherein said processing, calculating andproviding means includes and aircraft, on-board computer.

7. The tracker of claim 6 wherein said computer determines thedirection-cosines of the line between said first and second radiatingmeans from the outputs of said detecting means. 7

8. A method of determining the orientation of an object wherein firstand second wave radiating means are attached to the object at knownpositions and first, second, and third wave detecting means aresystemspatially fixed at known positions, comprising the steps of;

causing said first radiating means to radiate a wave,

measuring the time it takes for the wave radiated by said firstradiating means to travel to each of said detecting means,

causing said second radiating means to radiate a wave,

6 measuring the time it takes for the wave radiated by electronicallydetermining the directiomcosines desaid second radiating means to travelto each of fining the line joining the first and second radiating saiddetecting means, converting the times measured to respective distancemeasurements, 5

means from the distance measurements.

1. An acoustical tracker system for determining the position andorientation of an object, comprising: first and second means attached tosaid object for radiating ultrasonic waves; first, second, and thirdultrasonic wave detecting means systemspatially fixed for detecting saidradiated ultrasonic waves and providing outputs in response thereto; andmeans coupled to said radiating means and said detecting means forprocessing said detecting means outputs, electronically calculating thedistances from each said radiating means to each said detecting means,and providing an output of information defining the position andorientation of said object.
 2. The tracker of claim 1 wherein the pointsin space occupied by said first, second, and third detecting meansdefine a plane, and the second and third detecting means are equallyspaced from the first detecting means.
 3. The tracker of claim 1 whereinsaid object is an operators helmet and said tracker further comprises ahelmet mounted sight which is independent of operator eye movement, suchthat the tracker determines the orientation of the helmet and, thereby,the operator''s line-of-sight.
 4. The tracker of claim 3 wherein thepoints on the helmet occupied by said first and second radiating meansdefine a line which is parallel to the operator''s line-of-sight.
 5. Thetracker of claim 4 wherein the points in space occupied by said first,second, and third detecting means defines a plane, and the second andthird detecting means are equally spaced from the first detecting means.6. The tracker of claim 5 wherein said processing, calculating andproviding means includes and aircraft, on-board computer.
 7. The trackerof claim 6 wherein said computer determines the direction-cosines of theline between said first and second radiating means from the outputs ofsaid detecting means.
 8. A method of determining the orientation of anobject wherein first and second wave radiating means are attached to theobject at known positions and first, second, and third wave detectingmeans are system-spatially fixed at known positions, comprising thesteps of; causing said first radiating means to radiate a wave,measuring the time it takes for the wave radiated by said firstradiating means to travel to each of said detecting means, causing saidsecond radiating means to radiate a wave, measuring the time it takesfor the wave radiated by said second radiating means to travel to eachof said detecting means, converting the times measured to respectivedistance measurements, electronically determining the direction-cosinesdefining the line joining the first and second radiating means from thedistance measurements.